SOLUTION

a) gas as dry air , and contains  and .There gases do not radiate. Heat transfer occurs by forced convection only.



 

Heat loss per meter  

b) Heat transfer would occur both by convection and radiation. Oxygen and nitrogen are transparent to radiation but  vapor of air will radiate heat. Emissivity of hot gas =0.016

  
 
Substituting the values we get

.

Total heat transfer would consist of convection and radiation and is equal to

  

C) In this case heat transfer will occur both by convection and radiation

 



 

We note that heat transfer in gases becomes very high when the gas contains  and . The role of radiation is very large in comparison to convection. We see that if the gas contains  and , heat transfer is around  more than if gases do not contain  and .